In order to protect the global environment, low environmental load materials have been received attention, which have a low dependence on fossil fuels which are exhaustible resources and generate large amounts of carbon dioxide and air pollutants. Many low environmental load materials are known, and typical examples thereof may include polylactic acid, polyhydroxyalkanoates, polyamide 11, and the like. The vinyl chloride resin is also a low environmental load material, because 57% thereof is derived from a salt and it has a low dependence on fossil fuels; it has excellent mechanical properties and durability; and the hardness can be widely adjusted to ranges from hard to soft by addition of a plasticizer. The vinyl chloride resin, accordingly, have recently received attention again.
A soft vinyl chloride resin has the excellent mechanical properties and durability, but has a problem in which a large amount of a plasticizer is added. The plasticizer has not only defects of physical properties such as high plasticizer migration, bleeding out property, and volatility but also a defect in which a material suspected of being an environmental hormone is used as the plasticizer, and thus recently the improvement thereof has been advanced.
For example, polyester plasticizers whose molecular weight is increased to about several thousands to the first half of about several tens of thousands, classified into an oligomer, are known, although usually used plasticizers have a molecular weight of about several hundreds. The plasticizers above, however, cannot sufficiently reduce the plasticizer migration, the bleeding out property, and the volatility, and many of them have a problem in which they are derived from fossil fuels.
Patent Document 1 suggests a resin composition containing a polyhydroxyalkanoate oligomer and a vinyl chloride resin, but it has no Examples in which the vinyl chloride resin is used, and sufficient tensile elasticity and tensile elongation cannot be obtained in other Examples. In addition, polyhydroxyalkanoate oligomers having a molecular weight of 25000 or less are mainly used, and such oligomers have problems of the comparatively high plasticizer migration, bleeding-out property, and volatility, as with the polyester plasticizer, because of the comparatively small molecular weight of the oligomer.
On the other hand, Patent Document 2 is an example in which excellent compatibility with the vinyl chloride resin is realized while the molecular weight is as high as a resin, i.e., from the latter half of several tens of thousands to several hundreds of thousands; which discloses a copolyester polymer containing long chain ester units derived from a long chain glycol having a molecular weight of 600 to 6000 and a dicarboxylic acid having a molecular weight of less than 300, and short chain ester units derived from a diol having a molecular weight of less than 250 and a dicarboxylic acid having a molecular weight of less than 300.
The copolyester polymer described above has a sufficient high molecular weight, and thus has the low plasticizer migration, bleeding out property, and volatility, but its starting materials are derived from fossil fuels, and further improvements are required. In addition, Patent Document 2 has neither description of transparency nor uses which require the transparency at all, and thus it can be considered that the transparency of the copolyester polymer may be insufficient.
On the other hand, Patent Document 3 discloses a resin composition containing a vinyl chloride resin, a polyester resin, and an acrylic polymer. Patent Document 3 is a technique directed to a fiber having increased heat-resistance by improving a thermal shrinkage upon a secondary processing, and a melting point of the polyester resin is set so that it can impart the excellent heat-resistance in a forming temperature range of the vinyl chloride resin, whereby the comparatively better heat-resistance at the melting point can be realized after the molding. However, the polyester resins actually used in Patent Document 3, such as a polylactic acid resin and a crystalline polyester resin, are not suitable for softening the vinyl chloride resin.